The present invention relates to plasma processing technology for performing such processing as micro-fabrication by dry etching, thin-film formation, and surface modification by utilizing plasma, to plasma generating technology for use in the plasma processing, and to RF-power applying technology for generating plasma.
In recent years, plasma processing technology has found a wide range of applications such as micro-fabrication by dry etching, thin-film formation, surface treatment such as surface modification for treating the surface of a material. The plasma processing technology is particularly useful in the field of semiconductor, since it is essential to the manufacture of ultralarge-scale integrated circuits.
Conventionally, an inductively-coupled parallel-plate plasma generating apparatus has been used widely for plasma processing. This is because the foregoing apparatus is capable of easily generating a uniform, low-density plasma under comparatively low pressure, which satisfies the demand for equal plasma processing. However, the recent tendency toward increasingly miniaturized semiconductor integrated circuits has necessitated the generation of a high-density plasma under extremely low pressure. As a result, attention is being given to an inductively-coupled plasma generating apparatus which generates a plasma by applying an induction field formed with an RF current flowing through a coil to a space under reduced pressure as well as a plasma processing apparatus using the inductively-coupled apparatus for generating plasma.
By way of example, conventional inductively-coupled plasma processing apparatus will be described with reference to the drawings.
FIG. 18 is a schematic view of an inductively-coupled plasma processing apparatus according to a first conventional embodiment. In the drawing is shown a cylindrical chamber 101 having its inside held under a specified pressure. The chamber 101 is provided with gas introducing means, exhaust means, and carrying means for carrying an object to be processed in and out of the chamber 101, each of which is not shown.
On the bottom of the chamber 101, there is provided a lower electrode (sample stage) 103 with intervention of an insulator 102. The lower electrode 103 supports the object 104 to be processed such as a semiconductor wafer, which is subjected to etching or film deposition.
Above the chamber 101, there are provided a first RF (Radio-Frequency) power source 105 and a single flat, spiral coil 106 having one terminal grounded. The first RF power source 105 is connected to the other terminal of the spiral coil 106 via an impedance matcher 107. Below the chamber 101, there is provided a second RF power source 108. The second RF power source 108 is electrically insulated from the chamber 101 and the insulator 102, while it is electrically connected to the lower electrode 103. The second RF power source 108 applies an RF bias voltage to a plasma generated in the chamber 101. For safety, the ground potential of each of the first and second RF power sources 105 and 108 and the ground potential of the spiral coil 106 are adjusted to be equal to the ground potential of the chamber 101.
A description will be given below to a method of performing plasma processing by using the intuitively-coupled plasma processing apparatus according to the first conventional embodiment.
Initially, the object 104 to be processed is carried in the chamber 101 by the carrying means (not shown). Thereafter, gas is introduced into the chamber 101 by the gas introducing means (not shown) and exhausted from the chamber 101 by the exhaust means (not shown), thereby holding the inside of the chamber 101 under a specified pressure.
Subsequently, RF power from the first RF power source 105 is applied to the spiral coil 106, while RF power from the second RF power source 108 is applied to the lower electrode 103. The RF power supplied to the spiral coil 106 permits an RF current to flow through the spiral coil 106 and an alternating field generated by the RF current affects the space inside the chamber 101, so that electrons present in the space inside the chamber 101 move in such a direction as to generate a magnetic field that counteracts the magnetic field generated around the spiral coil 106. The movement of the electrons caused by inductive coupling changes the gas in the chamber 101 into a plasma. In this case, since the impedance matcher 107 performs impedance matching, a stable plasma discharge is caused.
By causing the plasma generated in the chamber 101 to act on the object 104 to be processed, there can be achieved surface modification of the object 104 to be processed such as surface oxidation, surface nitridation or impurity doping, thin film formation on the surface of the object 104 to be processed, and isotropic dry etching.
By utilizing Vpp (Peak-to-Peak voltage) and Vdc (dc potential at the lower electrode 103) generated by an alternating bias voltage applied by the second RF power source 108 to the lower electrode 103, ions in the plasma are effectively directed to the object 104 to be processed, which enables micro-fabrication by anisotropic dry etching.
The supply of the RF power from the first and second RF power sources 105 and 108 is completed at the time at which the processing of the object 104 is completed. After that, the introduction of the gas into the chamber 101 is terminated and the gas remaining in the chamber 101 is exhausted therefrom. Then, the object 104 to be processed is retrieved from the chamber 101, whereby the plasma processing is completed.
FIG. 19 is a schematic view of an inductively-coupled plasma processing apparatus according to a second conventional embodiment. In FIG. 19, the description of like components used in the inductively-coupled plasma processing apparatus according to the first conventional embodiment shown in FIG. 18 is omitted by providing the same reference numerals. In the second conventional embodiment, a helical coil 109 instead of the spiral coil 106 used in the first conventional embodiment is provided around the circumference of the chamber 101. A method of performing plasma processing by using the inductively-coupled plasma processing apparatus according to the second conventional embodiment is the same as in the first conventional embodiment.
FIG. 20 is a schematic view of the inductively-coupled plasma processing apparatus according to a third conventional embodiment. In FIG. 20, the description of like components used in the inductively-coupled plasma processing apparatus used in the first conventional embodiment is omitted by providing the same reference numerals. In the third conventional embodiment, a multiple spiral coil 110 consisting of four coils connected in parallel is provided instead of the single spiral coil 106 used in the first conventional embodiment. A method of performing plasma processing by using the inductively-coupled plasma processing apparatus according to the third conventional embodiment is the same as in the first conventional embodiment.
In the first and second conventional embodiments, if RF power at a frequency higher than 13.56 MHz is applied to the spiral coil 106 or helical coil 109 to control the electron temperature of the plasma, the reactance (j.omega.L: where j is an imaginary unit; .omega. is the angular frequency of RF power; and L is the inductance of a coil) of the spiral coil 106 or helical coil 109 is increased, so that it becomes difficult to perform impedance matching and hence a plasma discharge is less likely to occur.
To generate a plasma excellently uniform over a large area in the first and second conventional embodiments, the lengths and diameters of the spiral coil 106 and helical coil 109 should be increased, so that the inductance and reactance thereof are inevitably increased.
The third conventional embodiment has been proposed to overcome the foregoing problems, in which the multiple spiral coil 110 is provided in place of the spiral coil 106 provided in the first conventional embodiment, thereby reducing the impedance of the coil. Since impedance matching is performed more easily, a plasma discharge is more likely to occur.
However, in the case of using radio-frequency power in the VHF band at a high frequency of about 30 to 300 MHz to control the electron temperature of the plasma in the inductively-coupled plasma processing apparatus according to the third conventional embodiment, there arises the problem that it is difficult to generate a plasma under a pressure lower than about 20 mTorr.
Therefore, the conventional inductively-coupled plasma processing apparatus is disadvantageous in that it cannot perform excellently equal plasma processing with high precision and reduced damage, since a high-density plasma cannot be generated under extremely low pressure when RF power at a high frequency is applied to control the electron temperature of the plasma.